A conventional type of apparatus for the continuous casting of metals includes a cooled, generally vertical mold into which molten metal is continuously introduced from a suitable teeming vessel, e.g. a tundish. The molten metal adjacent the cooled walls of the mold solidifies thereby forming a shell which contains a molten core. The shell and its molten core are continuously withdrawn from the mold via a suitable withdrawal mechanism thus generating a long strand which is guided along a path curving towards the horizontal. Outside of the mold, the strand is subjected to the direct action of a coolant so that the molten core progressively solidifies as the strand moves along the path. After complete solidification, the strand is cut into sections which may be stored on a cooling bed or fed directly into a mill for further processing.
The mold forms part of a mold assembly which is supported on a mold table. The design of the mold assembly varies depending upon the cross-sectional area of the strand being cast but is invariable in that only a single mold is incorporated in the mold assembly.
For strands of relatively small cross-sectional area, the mold is in the form of a thermally conductive tube which is normally composed of copper. The mold assembly includes a cooling jacket which surrounds the mold circumferentially. The ends of the cooling jacket are closed by means of plates provided with openings which respectively register with the inlet and outlet openings of the mold. The mold is supported by the cooling jacket and the end plates of the cooling jacket are removable so as to permit the mold to be interchanged.
The cooling jacket has an inlet and an outlet for coolant and a baffle is arranged between the inner wall of the cooling jacket and the outer wall of the mold to direct the flow of coolant within the cooling jacket. The baffle is provided with a horizontal, annular flange on the outer surface thereof and this flange faces another horizontal flange provided on the inner surface of the cooling jacket. A seal is arranged between the two flanges. The coolant inlet is located below the flanges whereas the coolant outlet is located above the flanges. The flanges divert the coolant entering the cooling jacket around the lower end of the baffle to the interior thereof where the coolant travels upwardly in contact with the mold and around the upper end of the baffle to the coolant outlet.
For strands of relatively large cross-sectional area, the mold is made up of individual, thermally conductive plates which are normally composed of copper. The mold assembly includes back-up plates which are usually made of steel and the number of back-up plates equals the number of copper plates. One copper plate is mounted on each back-up plate. The individual sets consisting of back-up plate and copper plate are held together in the desired configuration by means of bolts.
The faces of the copper plates which abut the back-up plates are formed with channels which are intended for the circulation of coolant. The back-up plates have inlet and outlet conduits which open to the channels and coolant enters and leaves the channels in the copper plates via the back-up plates.
The mold is subject to wear due to the abrasive effect which arises as the strand moves through the mold. The abrasive effect of the strand results in marks on the inner surface of the mold which, in turn, affect the quality of the strand surface. When the marks on the inner surface of the mold become sufficiently pronounced, it is necessary to change the mold. It also becomes necessary to change the mold when a change in the cross-sectional configuration and/or dimensions of the strand is desired. Furthermore, if the mold is tapered, a mold change may be required when the metal being cast is replaced by one having different shrinkage characteristics.
In order to change the mold, the entire mold assembly must be detached from the mold table and removed from the casting apparatus. A new mold assembly is then inserted in the apparatus. This operation is cumbersome and time-consuming since the fasteners which secure the original mold assembly on the mold table must be removed and a crane or other lifting mechanism must be brought into position to lift the mold assembly and transport it from the vicinity of the mold table. The steps required to remove the original mold assembly from the casting apparatus must thereafter be repeated in reverse for the new mold assembly.
Another problem involved in changing a mold resides in that this cannot be accomplished while the teeming vessel which admits the molten metal into the mold remains in position. This poses a particular disadvantage in multistrand continuous casting installations where a single teeming vessel admits molten metal into a plurality of molds simultaneously. Should one of the molds become defective during a cast, it is necessary either to discontinue the flow of molten metal into the defective mold for the duration of the cast or to abort the entire cast in order to permit replacement of the defective mold. In the former case, the production rate is decreased and, in addition, there arises the possibility that a portion of the heat being cast may have to be discarded due to the fact that the reduced casting rate may not suffice to permit casting of the entire heat before solidification. In the latter case, the portion of the heat remaining at the time a mold becomes defective has either to be discarded or cast into conventional ingot molds which have well-known disadvantages.
In order to reduce the time which is required to change a mold, it has been proposed to mount a pair of mold assemblies on a turntable. The turntable is so arranged that one of the mold assemblies is in the casting position while the other of the mold assemblies is in a preparation position. When the mold in the casting position must be replaced, the turntable is rotated so that the mold assembly in the preparation position is brought into the casting position while the mold assembly originally in the casting position is brought into the preparation position. The mold assembly now in the preparation position may be replaced with a fresh mold assembly while casting proceeds with the mold assembly which has been rotated into the casting position.
A related proposal contemplates a pair of mold assemblies which are displaceable between a casting position and a preparation position along a linear path.
While the above proposals do reduce the time required to change a mold, there is the disadvantage that a relatively large amount of space is required. These proposals thus cannot be applied where space is limited and are also not well-suited for multistrand installations since the application thereof to each mold of such an installation would result in an unacceptable increase in size of the installation. Furthermore, casting apparatus utilizing the above proposals, as well as earlier casting apparatus, require that a substantial number of complete mold assemblies be kept on hand at all times to prevent interruptions of undue length in casting. This is especially true for casting apparatus which are designed to cast strands of various cross-sections.